1. Field of the Invention
This application relates generally to devices for converting a part of the energy of a flowing fluid such as wind into mechanical energy, which is used, in turn, to drive devices such as alternators or generators.
2. Description of the Prior Art
As fossil fuel supplies dwindle, renewable energy sources will be called upon more and more to produce power. One ubiquitous source of renewable energy is wind. Even a gentle breeze has substantial energy, and wind energy increases exponentially with wind velocity. Thus, a wind of eleven miles per hour has one-third more energy than a wind of ten miles per hour.
The class of devices which attempt to capture and utilize wind energy are known generically as wind motors. The best known device of this class, the common windmill, has been used for centuries to derive mechanical energy from wind. The typical windmill has a set of blade-like vanes projecting radially from the end of a horizontal shaft. These vanes are elevated atop a supporting tower. The vanes and their associated horizontal shaft are free to rotate about a vertical axis so that a rudder-like arrangement can keep the vanes facing into the prevailing wind. The vanes are twisted in a manner which causes wind to impart a torque and hence a rotational motion to them. The turning of the vanes turns the horizontal shaft which is typically geared to a vertical shaft which transmits the rotational energy to the ground level.
It is known in the art to mount on the same support a second set of blade-like vanes directly downwind of the first set, with the vanes twisted in an opposite fashion to cause rotation in a direction opposite that of the first set. These counter-rotating props may be connected to a generator or alternator. Such a wind motor is available commercially from Energy Division, Inc., of Miami, Florida.
A more contemporaneous version of the wind motor operates with props or other suitable wind force collectors projecting radially in a horizontal plane from a vertically disposed central shaft or support. Wind force collectors on the wind motor move with the wind for half of a rotation and against the wind during the other half of a rotation. In order for wind to create a net force imbalance, wind force collectors must present more aerodynamic resistance while moving with the wind than while moving against the wind. It is well known to devise such wind force collectors by taking advantage of the fact that wind force collectors rotating in a horizontal plane present one profile while moving with the wind and the opposing profile while moving against the wind. Accordingly, wind force collectors have been provided with wind traps shaped as cups or as hemispheres, whose open sides having high aerodynamic drag, face into the wind when moving with it and whose closed sides, having relatively low aerodynamic drag, face the wind when moving against it. The term wind trap is used to connote any structure affixed to or integral with a wind force collector which performs the function of capturing wind.
Wind traps have also been described which move to a low wind-resistance position during the half cycle in which they move against the wind. A device constructed along these lines is disclosed in U.S. Pat. No. 3,897,170 to Darvishian.
Wind traps as described above have one-half cycle of rotation when they move against the wind, with their low-drag profile facing the wind (their resistive half-cycle), and the other half-cycle when they move with the wind with their high-drag profile facing the wind (their power half-cycle). It is important to note that in the resistive half-cycle, any aerodynamic drag caused by the wind trap reduces the net torque, and hence the net power, produced by the device.